The present invention pertains to electromagnetic emissions and more particularly to an arrangement for shielding printed circuit boards from electromagnetic emissions.
Today""s printed circuit boards (PCBs) are complex, multi-layered structures on which highly integrated electronic circuitry is affixed and connected. Various circuit functions such as processors, memory, etc. often operate at high frequencies and generate considerable electromagnetic fields and interference. These fields and interference may affect other circuit functions which are located upon the printed circuit board or nearby located printed circuit boards. Further, in an effort to highly concentrate and miniaturize electronic circuitry and equipment required for the implementation of various functions, PCBs may be located near one another. Thereby, one PCB may be subjected to the electromagnetic emissions of a closely located PCB.
Current solutions to the problem of electromagnetic emissions involve shielding circuitry on a PCB from other circuitry on the same PCB or closely located PCBs. Removable shields pose a particular problem since they can not easily be soldered. A current solution to this problem involves bolting a metallic shield over the affected PCB or portion of the PCB. This solution includes a metallic shield which has a cavity to fit over the affected circuitry. This shield provides for diminishing electromagnetic emissions both from the circuit outward and to the circuit from outside sources or other circuits.
Current solutions to the electromagnetic shielding problem typically involves sealing the lid which has a cavity or cavities to the printed circuit board. This seal is typically achieved by providing a pliable conductive gasket material which is positioned at the interface between the PCB and the lid to facilitate electrical contact and continuity between the shield and the surface of the PCB. The gasket material is expensive and requires extra production steps to apply the gasket material appropriately between the lid and the PCB. The gasket material presents further problems in that over time the gasket material degrades due to corrosion. In addition the gasket material deforms and loses its pliability. Each of these deficiencies leads to higher electromagnetic emissions than can be tolerated by circuitry. As a result the performance of the circuitry may deteriorate over time along with the gasket material.
What is needed is a shielding arrangement which eliminates the need for the pliable gasket material, thereby reducing costs while simultaneously providing better electromagnetic shielding of emissions.